1. Technical Field
The invention relates to the field of systems for irradiating articles. In particular, the invention relates to shielding for article irradiation systems.
2. Description of Related Art
Radiation is used to treat many types of articles. The types of radiation used include, for example, x-rays, gamma rays, and electron particles. The types of articles treated with radiation are many and varied. For example, radiation is used to treat silicon chips, polymers, medical devices, and, more recently, food products. For example, the Food and Drug Administration and the Center for Disease Control have both supported the irradiation of food products for controlling or eliminating microorganisms in food products.
Irradiation systems often employ high levels of radiation to treat articles, with article irradiation being performed in a cell area surrounded by radiation shielding. The radiation is generated by a radiation source housed within the irradiation system. During irradiation, products are typically conveyed into an irradiation system on a conveyor system or other continuous loading system, the loading system transporting articles through the cell area for irradiation, and then out of the irradiation system for unloading. Many states regulate the emission of radiation from irradiation systems, and the radiation shielding is designed to control emissions so that they conform to government requirements.
In order to conform to emission requirements, one type of conventional irradiation system utilizes a xe2x80x9cpoured in placexe2x80x9d steel-reinforced concrete design as a radiation shield. Poured in place structures, while effective in controlling the escape of radiation, are large and time-consuming to construct. For example, when using concrete fill, radiation shield wall thicknesses of up to 12 feet may be required. In addition, the steel-reinforced concrete structures are permanent structures, which limits the flexibility of the site housing the irradiation system.
The use of large, permanent shield structures is aggravated by the need to shield certain parts of the irradiation system, such as the continuous loading system, the cell area, and the radiation source. The parts of the irradiation system occupy a large surface area at the irradiation site, and the requirement for a large irradiation site results in high overhead costs.
A permanent shield structure is also impedes access to the interior of the irradiation system. It may therefore be necessary to remove certain elements within the shield structure by crane, or other lifting device.
There is therefore a need for an irradiation system that occupies a reduced area. There is also a need for an irradiation system that provides flexibility for the site housing the irradiation system, and for ease of access to the interior of the irradiation system.
The present invention overcomes the shortcomings of the conventional art and may achieve other advantages not contemplated by conventional devices.
According to a first aspect of the invention, an irradiation system includes a radiation source arranged to emit a radiation beam along at least one beam path extending from the radiation source, with an inner shield disposed around the radiation source for attenuating radiation generated by the radiation source, and the beam path extending through at least one path aperture in the inner shield. A first conveyor system is provided for transporting articles through the beam path, and an outer shield is disposed around the inner shield and the first conveyor system for attenuating radiation generated by the radiation source.
According to the first aspect, radiation generated by the radiation source must escape frorn both the inner shield and the outer shield in order to escape the irradiation system. The first conveyor system is disposed between the inner shield and the outer shield, which reduces the total space occupied by the irradiation system.
According to a second aspect of the invention, an irradiation system is arranged in an upper level and a lower level, the system including a radiation source in the upper level arranged to emit radiation along first and second beam paths for irradiating articles on the upper level, and to emit radiation along a third beam path for irradiating articles on the lower level. An upper level shield is disposed around the radiation source for attenuating radiation generated by the radiation source, and a first conveyor system is provided for transporting articles through the first and second beam paths. On the lower level, a second conveyor system transports articles through the second beam path.
According to the second aspect, the radiation source can irradiate articles on both an upper level and a lower level of the irradiation system, which reduces the space required for the irradiation system. In addition, the shield requirements of the irradiation system are reduced due to the arrangement of the irradiation system into an upper and a lower level.
According to a third aspect of the invention, a method of removing a radiation source from an irradiation system includes disconnecting a removable module of an outer shield from the outer shield, disconnecting a removable module of an inner shield from the inner shield, and removing the radiation source from the irradiation system through openings left by the removable modules.
According to the third aspect, the irradiation source can be laterally removed from the irradiation system, without removing permanent walls or other fixed structures. Lateral removal through the inner and outer shields avoids the more difficult method of vertical removal using cranes or similar lifting devices.